You can add Google Photos to your frame using the Google Photos integration in the Aura App. When you open the Aura App, scroll down to where you see "Google Photos - Link Account" and select "Add Account." You are then invited to enter your Gmail address and password. Once this is complete you'll have access to all your Google Photos.
As long as your photos are stored in your iCloud or Google Photos library, it will sync with the frame (the photos don't necessarily need to be stored locally on your phone). Google photos offers free unlimited storage, so you can save your entire photo collection from your computer to Google Photos, which can then be shared to the frame.
Please note that there is a limit to the number of Google Photos per album we are able to import to the Aura App. The max is 10,000 photos per album. Additionally, any shared Google Albums will not appear in the Aura App. This is a limitation in how the Google Photos application integrates with our app, and unfortunately we can't adjust this to allow for unlimited photos to be synced using Google Photos. If you have more than 10,000 photos in a Google Photos album, we suggest you break your photos into multiple albums with fewer photos than 10,000 each.
Please reach out to firstname.lastname@example.org with any questions or issues using Google Photos with Aura.